The invention relates to a synchronizing mechanism for a gearbox, including a driving disc which is non-rotatably mounted on a shaft and is surrounded by a clutch collar non-rotatably connected to the disc, the clutch collar being axially displaceable for engaging with a gear rotatably mounted on the shaft, during which engagement there is coaction with the synchronizing mechanism.
In gearboxes, it is usual to arrange a plurality of gears rotatably mounted on a shaft and in constant mesh with a corresponding number of gears rigidly attached to another shaft. Different gear ratios for the gearbox are obtained by alternatively engaging the rotatably mounted gears with their shaft. With the object of facilitating such engagements, it is usual to arrange synchronizing mechanisms, functioning during gear-changing operations such as to enable the gear which is to be engaged with the shaft to be given the same rotational velocity as the shaft before engagement takes place. Such synchronizing mechanisms can be implemented in different ways, but usually the elements which are to be mutually engaged are each provided with a conical friction surface. By axial displacement of at least one of the elements, the friction surfaces are brought into such gliding and engagement against each other that the elements assume the same rotational velocity.
For preventing during synchronizing phases that engagement takes place before velocity equilibrium has been obtained, the synchronizing mechanism also includes detent elements. A usual form of such a detent element comprises circumferentially arranged teeth on one of the so-called synchronizing rings, said teeth assuming a detent position during the angular movement of the synchronizing ring during the synchronizing phase such as to prevent axial displacement of a clutch collar non-rotatably mounted on the shaft. The teeth on the synchronizing ring are formed with sloping end surfaces which abut complementally sloping end surfaces on the detent teeth on the clutch collar. After synchronization has been attained, the axial force of the clutch collar is sufficient to give, via the sloping end surfaces, the synchronizing ring an angular movement into a non-detent position such that the clutch collar may be axially displaced into engagement with detent teeth on the relevant gear in the gearbox.
The slope of the teeth end surfaces is dimensioned against the background that a more acute inclination of the surfaces results in less force being required for engagement after synchronization, while a more obtuse slope results in a more reliable detent action during the synchronizing phase. As a rule, the latter situation has higher priority, this resulting in the drawback with the gearbox that gear-changing can be experienced as heavy. In dimensioning synchronizing mechanisms, rapid and smooth synchronization is often striven for as well as low operating forces. In gearboxes for heavy vehicles, for example, there are large forces and moments which require great consideration. To achieve a large synchronizing torque from a limited operating force and also to keep the dimensions within reasonable limits, it is known to arrange a plurality of synchronizing rings in the same synchronizing mechanism. Two synchronizing rings are usually used in such a case, an outer ring formed according to the same principle as described above and an inner ring which is non-rotatably attached to a driving member on the shaft. Both synchronizing rings have their friction surfaces acting on a friction ring non-rotatably attached to the gear and between the two synchronizing rings. The friction ring is formed with both an outer and an inner friction surface.
Synchronization with two synchronizing rings is often called double-cone synchronization, and the apparatus for performing a double-cone synchronizing mechanism. A disadvantage with the double-cone synchronizing mechanism is that only the outer synchronizing ring is formed with detent teeth. The torque acting on the outer synchronizing ring during the synchronizing phase is only a part of the total torque, i.e. the so-called synchronizing torque, which acts between the participating units. To ensure detent action during synchronization, it is therefore required that the angle between the surfaces of the teeth is formed relatively obtuse. However, this results in the drawback mentioned above, which is that great force is required for engagement and that the gear-changing action of the gearbox may be experienced as heavy.